1. Field of the Invention
The present invention relates to a vibration isolating apparatus which prevents vibrations from being transmitted from a member which generates vibrations. This device can be applied to, for example, cases in which the transmission of vibrations from an engine mounted in a vehicle is to be prevented, or the like.
2. Description of the Related Art
As a vibration isolating apparatus, a structure is known which, for example, is disposed as an engine mount between an engine of a vehicle, which is a vibration generating portion, and the vehicle body, which is a vibration receiving portion, and which absorbs the vibrations generated by the engine so as to impede transmission of vibrations to the vehicle body.
An example of such a vibration isolating apparatus is the bush-type apparatus shown in FIG. 4. This conventional vibration isolating apparatus will be described concretely hereinafter on the basis of FIG. 4.
In the vibration isolating apparatus, an inner tube 114 is disposed, via an elastic body 116, at the inner side of an outer tube 112 which is tubular and forms an outer frame. Further, a main fluid chamber 116, and auxiliary fluid chambers 120, 122, which communicate with the main fluid chamber 118 by orifices 124, 126 which are passages, are formed.
A diaphragm 128, which is an elastic membrane made of rubber, forms a portion of a partitioning wall of the auxiliary fluid chamber 120. The space between the diaphragm 128 and the outer tube 112 is an air chamber 130. A through hole 132 is formed in a portion of the outer tube 112 which portion opposes the diaphragm 128.
Accordingly, when the engines which is mounted to the vibration isolating device, vibrates and vibrations are generated, the vibrations are absorbed or the vibrations are damped by the fluid column resonance or the like of the fluid within the orifices 124, 126 serving as low dynamic springs which communicate the main fluid chamber 118 and the auxiliary fluid chambers 120, 122, respectively. The transmission of vibrations to the vehicle body is thereby impeded.
However, in the above-described vibration isolating apparatus which impedes the transmission of vibrations by utilizing fluid column resonance and lowering the dynamic spring constant, the flow resistance of the orifice through which the fluid flows is set in accordance with the frequency of the vibrations to be absorbed. Thus, the flow resistance depends on the frequency of the vibrations.
Namely, in a conventional vibration isolating apparatus, there are two types of passages which are the orifice 124, which is a passage for absorbing idle vibrations, and the orifice 126, which is a passage for absorbing booming-noise vibrations. The orifices 124, 126 prevent the transmission of vibrations of two frequencies.
However, vibrations of intermediate frequencies between the idle vibration region and the booming-noise vibration region, which is a higher frequency region than the idle vibration region, are not absorbed in either passage. Thus, there is the drawback that the frequency region between the idle vibration region and the booming-noise vibration region has a high dynamic spring constant, and the vibrations cannot be reduced.
Accordingly, it has been thought to increase the number of passages to decrease the dynamic spring constant in the above-mentioned frequency region. For example, a structure in which two passages are provided for one auxiliary fluid chamber is disclosed in Japanese Patent Application Laid-Open (JP-A) No. 7-233848.
However, in accordance with the structure disclosed in the aforementioned publication, as the peak-shaped frequency characteristic of the dynamic spring constant is shifted and becomes a broader characteristic, vibrations over a wide range of frequencies can be absorbed, but the spring constant of the frequency region between the idle vibration region and the booming-noise vibration region cannot be greatly decreased.
In view of the aforementioned, an object of the present invention is to provide a vibration isolating apparatus which can reduce vibrations even at frequencies between the idle vibration region and the booming-noise vibration region.
A vibration isolating apparatus relating to a first aspect of the present invention comprises: an outer tube which is tubular and which is connected to one of a vibration generating portion and a vibration receiving portion; an inner tube which is disposed at an inner peripheral side of the outer tube and which is connected to another of the vibration generating portion and the vibration receiving portion; an elastic body which is disposed between the outer tube and the inner tube and is elastically deformable; a main fluid chamber which contains a fluid with the elastic body serving as a portion of a partitioning wall of the main fluid chamber, and whose internal volume changes due to deformation of the elastic body; a first auxiliary fluid chamber which contains a fluid, at least a portion of a partitioning wall of the first auxiliary fluid chamber being elastically deformable; a diaphragm forming a portion of the elastically deformable partitioning wall of the first auxiliary fluid chamber, so as to expand and contract a space between the first auxiliary fluid chamber and the outer tube; a first passage which communicates the main fluid chamber and the first auxiliary fluid chamber; and a second passage which communicates the main fluid chamber and the first auxiliary fluid chamber, a passage sectional area of at least a portion of the second passage being smaller than a passage sectional area of the first passage, and a flow resistance of the second passage being smaller than a flow resistance of the first passage, wherein in a state in which internal pressure of the first auxiliary fluid chamber is low and there is little fluid within the first auxiliary fluid chamber, the diaphragm has a configuration which is sunk toward the first auxiliary fluid chamber, and in a state in which the internal pressure of the first auxiliary fluid chamber is high and there is much fluid in the first auxiliary fluid chamber, the diaphragm has a swollen configuration, and as the internal pressure of the first auxiliary fluid chamber rises and fluid flows into the first auxiliary fluid chamber, the diaphragm inverts and deforms into the swollen configuration.
In accordance with this structure, when vibrations are transmitted from the vibration generating portion which is connected to either the outer tube or the inner tube, the elastic body deforms, and the vibrations are damped by the elastic body. As the internal volume of the main fluid chamber changes due to the deformation of the elastic body, the fluid actively flows to the first auxiliary fluid chamber via the first passage. As a result, a change in pressure arises in the fluid within the first passage, and accompanying this change in pressure, the diaphragm, which is at least one portion of the partitioning wall of the first auxiliary fluid chamber, elastically deforms and the first auxiliary fluid chamber expands and contracts.
Namely, when vibrations are transmitted from the vibration generating portion, not only does the elastic body deform, but also, the dynamic spring constant decreases due to the first passage which connects the main fluid chamber and the first auxiliary fluid chamber. The vibrations are absorbed, and it is difficult for vibrations to be transmitted to the vibration receiving portion which is connected to one of the inner tube and the outer tube.
Moreover, not only the first passage, but the second passage as well also communicates with the main fluid chamber and the first auxiliary fluid chamber. The passage sectional area of at least a portion of the second passage is smaller than the passage sectional area of the first passage, and the flow resistance of the second passage is smaller than the flow resistance of the first passage.
Namely, the value of the passage sectional area/passage length, which is a value of the magnitude of the passage sectional area with respect to the passage length, of the second passage is greater than that of the first passage, and the flow resistance of the second passage is less than the flow resistance of the first passage. Vibrations over a wide range of frequencies can thereby be absorbed
The passage sectional area of at least a portion of the second passage is smaller than the passage sectional area of the first passage. Thus, when vibrations of a frequency which causes fluid column resonance in the first passage are generated, the fluid in the second passage barely moves back and forth at all, and the vibrations can be reliably absorbed by the fluid column resonance in the first passage.
The diaphragm forms a portion of an elastically deformable partitioning wall of the first auxiliary fluid chamber, and is in a form which expands and contracts the space between the first auxiliary fluid chamber and the outer tube. In a state in which the internal pressure of the first auxiliary fluid chamber is low and there is little fluid within the first auxiliary fluid chamber, the diaphragm has a configuration which is sunk toward the first auxiliary fluid chamber. In a state in which the internal pressure of the first auxiliary fluid chamber is high and there is much fluid within the first auxiliary fluid chamber, the diaphragm has a swollen configuration. As the internal pressure of the first auxiliary fluid chamber rises and fluid flows into the first auxiliary fluid chamber, the diaphragm inverts and deforms into the swollen configuration.
Namely, in the intermediate stage of deformation of the diaphragm, the diaphragm is in a structurally unstable state. Thus, the diaphragm is provided with an inverting function so as to be able to invert between a concave configuration and a convex configuration, and is made to be elastically deformable such that it is easy for the first auxiliary fluid chamber to expand and contract.
As a result, due to the diaphragm inverting due to elastic deformation, the internal pressure of the first auxiliary fluid chamber decreases, and the flow of fluid into the first auxiliary fluid chamber via the second passage can be promoted. Thus, vibrations can be absorbed even more effectively by the second passage in frequency regions other than the resonance region of the first passage. In accordance therewith, vibrations of frequencies in regions other than the resonance region of the first passage are absorbed in the second passage, and vibrations in regions other than the resonance region of the first passage can be reduced.
Further, in the vibration isolating apparatus of the present invention, preferably, further comprising an air chamber, which is provided between the diaphragm of the first auxiliary fluid chamber and the outer tube, and which is sealed.
Due to this structure, the movement of the inversion deformation of the diaphragm is generated by a balance between the rigidity characteristic of the diaphragm, the fluid pressure within the first auxiliary fluid chamber, and the air pressure within the air chamber. Accordingly, by making the air chamber a sealed space and making it easy for the diaphragm to deform and invert, it is easy for the first auxiliary fluid chamber to expand and contract as the diaphragm deforms.
Specifically, if the air chamber is not a closed space and communicates with the atmosphere, when the fluid pressure within the first auxiliary fluid chamber rises, the diaphragm deforms and swells toward the air chamber side, and closely contacts the outer tube side inner wall of the air chamber. Inversion deformation for returning to the original state does not arise until the fluid pressure falls.
In contrast, if the first air chamber is made to be a sealed space, when the fluid pressure within the first auxiliary fluid chamber rises, the air pressure within the air chamber rises as the diaphragm deforms and swells. When a certain pressure is reached, the diaphragm deforms and inverts toward the first auxiliary fluid chamber. However, the diaphragm does not closely contact the inner wall of the outer tube.
As described above, by making the air chamber a sealed space, the fluctuations in the air pressure within the air chamber, which fluctuations accompany the working of the air spring, can be utilized. In this way, the inversion movement of the diaphragm can be promoted, and the spring constant can be greatly decreased.
Moreover, preferably, the second passage has a hole portion which passes through between the main fluid chamber and a position along the first passage.
Due to this structure, merely by providing the small hole portion, which passes through between the main fluid chamber and a position along the first passage so as to form a short-cut, it is possible to form the second passage which commonly uses a portion of the first passage. In this way, it is possible to provide the second passage easily without using new parts for the passage.
As a result, while keeping the manufacturing costs of the vibration isolating apparatus down, vibrations of frequencies between the idle vibration region and the booming-noise vibration region can be absorbed and vibrations can be decrease.
The vibration isolating apparatus of the present invention preferably further comprises a second auxiliary fluid chamber which contains fluid, at least a portion of a partitioning wall of the second auxiliary fluid chamber being elastically deformable.
Further, preferably, the partitioning wall of the second auxiliary fluid chamber is formed by a diaphragm so as to expand and contract a space between the second auxiliary fluid chamber and the outer tube.
Furthermore, the vibration isolating apparatus preferably further comprises a third passage whose resonance frequency is different than resonance frequencies of the first passage and the second passage, the third passage being connected to the second auxiliary fluid chamber.
Moreover, preferably, the second auxiliary fluid chamber communicates with the main fluid chamber due to the first passage and the third passage being connected.
The present invention can be applied to a double-orifice-type vibration isolating apparatus having two passages which are orifices which connect the main fluid chamber and the first and second auxiliary fluid chambers, respectively. Vibrations of an even wider range of frequencies can thereby be reduced even more effectively.
In the vibration isolating apparatus of the present invention, preferably, the diaphragms of the first and second auxiliary fluid chambers are formed by membrane members made of rubber.
By making the diaphragm a membrane member formed of rubber, the diaphragm inverts and deforms even more easily, and even more effective and reliable vibration absorption in frequencies other than the frequency of the resonance region of the first passage is possible.
A vibration isolating apparatus relating to a second aspect of the present invention comprises: an outer tube which is tubular and which is connected to one of an engine and a vehicle body; an inner tube which is disposed at an inner peripheral side of the outer tube and which is connected to another of the engine and the vehicle body; an elastic body which is disposed between the outer tube and the inner tube and is elastically deformable; a main fluid chamber which contains a fluid with the elastic body serving as a portion of a partitioning wall of the main fluid chamber, and whose internal volume changes due to deformation of the elastic body; a first auxiliary fluid chamber which contains a fluid, at least a portion of a partitioning wall of the first auxiliary fluid chamber being elastically deformable; a diaphragm forming a portion of the elastically deformable partitioning wall of the first auxiliary fluid chamber, so as to expand and contract a space between the first auxiliary fluid chamber and the outer tube; a first passage which communicates the main fluid chamber and the first auxiliary fluid chamber; and a second passage which communicates the main fluid chamber and the first auxiliary fluid chamber, a passage sectional area of at least a portion of the second passage being smaller than a passage sectional area of the first passage, and a flow resistance of the second passage being smaller than a flow resistance of the first passage, wherein in a state in which internal pressure of the first auxiliary fluid chamber is low and there is little fluid within the first auxiliary fluid chamber, the diaphragm has a configuration which is sunk toward the first auxiliary fluid chamber, and in a state in which the internal pressure of the first auxiliary fluid chamber is high and there is much fluid in the first auxiliary fluid chamber, the diaphragm has a swollen configuration, and as the internal pressure of the first auxiliary fluid chamber rises and fluid flows into the first auxiliary fluid chamber, the diaphragm inverts and deforms into the swollen configuration.
The vibration isolating apparatus of the present invention preferably further comprises a second auxiliary fluid chamber which contains fluid, and at least a portion of a partitioning wall of the second auxiliary fluid chamber is formed by a diaphragm which is elastically deformable, and the diaphragm is structured so as to expand and contract a space between the second auxiliary fluid chamber and the outer tube.
Further, the vibration isolating apparatus preferably further comprises a third passage whose resonance frequency is different than resonance frequencies of the first passage and the second passage, the third passage being connected to the second auxiliary fluid chamber.
Moreover, preferably, the second auxiliary fluid chamber communicates with the main fluid chamber due to the first passage and the third passage being connected via a connecting passage whose passage sectional area is different than passage sectional areas of the first passage and the third passage.